Conversion of variable delivery pump to fixed delivery pump

ABSTRACT

A variable delivery fluid pump and a variable delivery fluid motor are used to accelerate the spindle of an inertia welding machine to the welding speed, and the pump is then converted to a fixed delivery pump in order to provide a nonfluctuating pressure to power the thrust cylinders for application of the welding pressure.

United States Patent Jozef Kiwalle;

Ira H. Sage, both of Peoria, 111. 27,903

Apr. 13, 1970 Dec. 7, 1971 Caterpillar Tractor Co. Peoria, 111.

Inventors Appl. No. Filed Patented Assignee CONVERSION OF VARIABLEDELIVERY PUMP T0 FIXED DELIVERY PUMP 5 Claims, 2 Drawing Figs.

US. Cl 417/218, 60/52 VS, 91/506 Int. Cl F04b 49/00 Field 01 Search417/212, 218; 91/506; 60/52 VS [56] References Cited UNITED STATESPATENTS 2,114,445 4/1938 Gros 74/839 3,139,006 6/1964 Budzich 91/5063,017,750 1/1962 Kempson 417/218 Primary Examiner-Carlton R. CroyleAssistant Examiner-Richard J. Sher Attorney-Fryer, Tjensvold, Feix,Phillips & Lempio ABSTRACT: A variable delivery fluid pump and avariable delivery fluid motor are used to accelerate the spindle of aninertia welding machine to the Welding speed, and the pump is thenconverted to a fixed delivery pump in order to provide a nonfluctuatingpressure to power the thrust cylinders for application of the weldingpressure.

ELECTRICAL CONTROLS TO MOTOR AND CYLINDERSL39 CONVERSION OF VARIABLEDELIVERY PUMP TO FIXED DELIVERY PUMP This invention relates to a controlfor a hydraulic pump of the kind in which the displacement of the pumpis varied by changing the angular position of a wobble plate. Thisinvention relates specifically to a control mechanism which functions toconvert the variable delivery pump to a fixed delivery pump on atemporary basis.

The present invention has particular utility in an inertia frictionwelding machine. In an inertia friction welding machine the energy forproducing the weld is stored in a rotating flywheel which is acceleratedto a selected rotational speed before the parts to be welded are engagedin rubbing contact.

In the present invention the flywheel is driven by a hydraulic motor.

The parts to be welded are pressed together by a hydraulically actuatedthrust cylinder.

A variable displacement hydraulic pump drives the hydraulic motor.

Alter the flywheel has been accelerated to speed, the pump is connectedto the thrust cylinder to produce the welding pressure.

A variable displacement pump is well suited for accelerating theflywheel, but is not entirely satisfactory as the power source for thethrust cylinders. The variable displacement pump presents problems ofpressure fluctuations resulting from the variable displacement featureof the fluid pump.

The problems of pressure fluctuations occuring during the thrust loadapplication have been severe enough to cause fixed displacement pumps tobe used in prior art machines. However a fixed displacement pumpcontributes a problem of its ownlow efficiency due to long accelerationtimes.

It is a primary object of the present invention to control thedisplacement of a variable displacement pump in a manner such that thepump can be operated as a variable displacement pump in one condition ofoperation and as a fixed displacement pump in a second condition ofoperation.

It is a related object to convert a variable displacement fluid pump toa fixed displacement pump during the second condition of operation byphysically locking the wobble plate of the pump in a predeterminedposition during the second condition of operation.

In accordance with the present invention the conversion means forconverting the variable delivery fluid pump to a fixed delivery fluidpump include the following specific items: A fluid locking cylinder; afloating piston within the cylinder; a second piston within the cylinderadjustable within the cylinder in relation to the desired deliveryposition of the pump piston; a rod within the cylinder and within thesecond piston securely fastened on one end to the second piston and inabutting relationship to the variable displacement pump servo piston onthe other end, and means to adjust the rod within the cylinder andwithin the second piston; valve control means to direct fluid to bothends of the locking cylinder at the same time, and separate valve meansto direct fluid to both ends of the cylinder controlling pumpdisplacement, electrical control means to activate both of the abovevalve control means at the same time; and a fixed delivery fluid pump tosupply fluid to the locking cylinder through the valve means describedabove.

A control for a hydraulic pump which incorporates the above notedfeatures and effective to function in the manner described constitutefurther specific objects of the present invention.

Other and further objects of the present invention will be apparent fromthe following description and claims and are illustrated in theaccompanying drawings which, by way of illustration, show preferredembodiments of the present invention and the principles thereof and whatare now considered to be the best modes contemplated for applying theseprinciples. Other embodiments of the invention embodying the same orequivalent principles may be used and structural changes may be made asdesired by those skilled in the art without departing from the presentinvention and the purview of the appended claims.

IN THE DRAWINGS FIG. 1 is a side elevation view of a friction welderconstructed in accordance with one embodiment of the present invention;and

FIG. 2 is a schematic view of a control constructed in accordance withone embodiment of the present invention and which can be used to converta variable delivery pump to a fixed delivery pump in the friction weldershown in FIG. I.

An inertia friction welding machine constructed in accordance with oneembodiment of the present invention is indicated generally by thereference numeral 11 in FIG. I.

The parts or workpieces to be welded by the friction welding machine 11are indicated by the reference characters WPI and WP2 in FIG. 1.

The part WPl is held in a chuck on a rotatable spindle 13.

The part WP2 is held in a chuck in a nonrotatable fixture 15.

The energy for producing the weld is stored in a rotating flywheel 17mounted on the spindle 13.

Loading means, in the form of one or more thrust cylinders 39, move thefixture 15 towards the rotating spindle 13 after the flywheel 17 hasbeen accelerated to the selected speed. The loading means cause theparts WP] and WP2 to be pressed together in rotating rubbing contact toproduce the welding pressure.

An electric motor I9 drives a hydraulic pump 36 to supply the power bothfor accelerating the flywheel to the selected rotational speed and foractuating the thrust cylinders 39 to provide the welding pressure.

The pump 36 is connected to a hydraulic motor 37 by a conduit 75 asshown in FIG. 1. The output of the pump 36 is also connected to thethrust cylinder 39.

The friction welding machine 11 incorporates an automatic control whichdirects the output of the pump 36 to the motor 37 until flywheel 17 isaccelerated to speed and which then directs the output of the pump tothe thrust cylinder 39.

The pump 36 is basically a variable displacement pump of the kind inwhich the displacement is varied by changing the angular position of awobble plate in the pump.

As noted above, it is desirable that the pump 36 function as a variabledelivery pump during the time the output of the pump is being deliveredto the motor 37 to accelerate the flywheel 17 to speed and then functionas a fixed displacement pump during the time that the output of the pumpis directed to the thrust cylinder 39 for producing the weldingpressure.

FIG. 2 illustrates in section the essential elements for converting avariable delivery fluid pump to a fixed delivery fluid pump. FIG. 2 alsoincludes some controls and elements in schematic form.

The conversion assembly 10 includes a cylinder 12, an adjustable stopshaft 14, a floating piston 16, and a fixed piston The stop shaft 14 andthe fixed piston 18 are fastened together by means of threads 20 and 22and are held in any given position by a lock nut 24.

A portion of the variable displacement pump controls is also shown inFIG. 2 and although not forming a portion of the conversion assembly,they are used in conjunction with the conversion assembly to accomplishthe desired result. These controls include a servo and pressurecompensating valve 26, a servo pressure cylinder 28, a servo piston 30,and a wobble plate rod 32 fastened at one end to the servo piston.

The wobble plate rod 32 is pivotally fastened at the other end to thewobble plate (shown in phantom line detail) which is used to change thedisplacement of the variable displacement fluid pump 36 (also shown inphantom line detail).

In the normal mode of operation of the variable delivery pump andcontrols (without the conversion assembly 10), a small constant deliverypump 38 delivers pressurized fluid to the servo and pressurecompensating valve 26 by means of line 76. The servo valve thenactivates the servo piston 30 by sending fluid to chamber 40 thru line42 or to chamber 44 thru line 46, depending on the high pressure signalwhich the servo valve is receiving from the main pump 36. The highpressure signal reflects the output pressure of pump 36 and reaches theservo valve 26 by means of line 74 and control valve 54. Movement of theservo piston 30, of course, changes the displacement of the variabledelivery pump 36 so that a delivery rate is produced in proportion tothe demand from the system.

The small pump 38 also supplies fluid from tank 78 to the main pump 36.The fluid is cleaned by means of filters 80 and Besides the assemblypreviously described, the conversion unit will include several otheritems for operation and control of the conversion assembly. Theseinclude a small constant delivery clamp pump 48, a control valve 50between pump 48 and the assembly 10, a control valve 52, and a controlvalve 54 between main pump 36 and the servo valve 26.

Besides providing power to operate the assembly 10, the small pump 48can be used to operate other machine functions which require small fluiddelivery.

The control valves 50, 52, and 54 are all connected to the electricalcontrols 56 of the machine and are automatically operated by suchcontrols when the spindle of the welding machine reaches a predeterminedand preset rotational velocity. However, override controls will beprovided to operate the conversion assembly manually if so desired.

To convert the variable delivery pump to a fixed delivery pump, thecylinder 28 of the servo assembly is altered to receive the conversionassembly 10 including the cylinder 12 which is sealed at each end bycaps 58 and 60. Cap 58 also serves to seal chamber 40 of servo cylinder28.

The adjustable stop shaft 14 is mounted for horizontal movement withinthe cylinder 12 and penetrates the end cap 58 in order to fasten to theservo piston 30 of the servo cylinder 28.

During the initial stages of the inertia weld cycle, the conversionassembly 10 and related controls are inactive and influence in no waythe normal functions of the variable delivery pump 36 including theservo and pressure compensating valve 26. The pump 36 therefore operatesto deliver a varying quantity of fluid in response to the signal fromthe servo valve 26, and piston 30 moves to the right or left withincylinder 28 in response to the servo valve 26 to change the displacementof the pump 36 by means of the wobble plate 34.

Although the adjustable stop shaft 14 is attached to the piston 30, noforce is applied to the shaft 14 at this time and piston 30 can merelymove the shaft 14 to the left if the servo piston 30 is signaled to movein that direction by the servo valve 26.

Since the adjustable'shaft 14 is fastened to piston 18 as previouslymentioned, any movement of the shaft 14 will cause the piston 18 to movealso; and likewise, any movement of piston 18 will cause movement ofshaft 14.

During the early stages of the acceleration cycle, piston 18 is free tomove within chamber 62 of the cylinder 12, and piston 16 is also free tomove within chamber 64 of the cylinder 12.

When the spindle of the welding machine reaches the predeterminedwelding velocity, the variable delivery controls of the pump 36 aredisabled and the conversion assembly 10 takes over to make the pump, inefi'ect, a constant delivery pump. To do this, a speed switch assemblysignals the electrical controls when the spindle reaches the weldingvelocity; and the electrical controls 56 in turn signal control valves50, 52, and 54 to shift to a new position.

Control valve 54 therefore closes off the high pressure signal from pump36 to the servo valve 26, and control valve 52 merely openscommunication between chamber 40 and chamber 44 of cylinder 28. Thisequalizes the pressure in chambers 40 and 44 and allows the piston 30 tobe shifted to any position within the cylinder by the shaft 14.

Shifting of valve 50 allows the pump 48 to be communicated to thecylinder 12 through line 66, and pressurized fluid enters chambers 62and 64 of cylinder 12 by means of passages 68 and 70.

Pressurized fluid will force the floating piston 16 to the left againstthe fixed stop member 72 and will also force the piston 18 to the rightagainst the floating piston 16.

Since the area of piston 16 under pressure is greater than the area ofpiston 18 under pressure, the piston 16 will be held against the stop72; and piston 18 will be held against piston 16 as long as pressureremains in chambers 62 and 64.

Since shah 14 is fastened to the piston 18, the position of shaft 14(and therefore the position of servo piston 30) is fixed in apredetermined position. This also predetermines the displacement offluid being delivered by the pump 36. The position of piston 30 (andtherefore the quantity of oil being delivered by pump 36 in a fixeddelivery position) can be altered by threading shaft 14 either in or outof the piston member 18 as previously described. This is, however, amanual adjustment and must be accomplished before the welding operationbegins.

Once the position and rate of delivery is determined, the piston 18 andshaft 14 are locked in the desired position by the locknut 24.

At the same moment that the pump 36 is converted from a variabledelivery pump to a fixed delivery pump, flow of fluid from pump 36 tothe spindle motor is discontinued; and flow is communicated to thewelding thrust cylinder of the welding machine. The welding thrustcylinder can then apply a constant nonfluctuating force to the weldpieces in order to accomplish a good weld.

If the variable delivery pump is used to supply power to the thrustcylinder without the use of a conversion unit, the force applied to thethrust cylinders by the pump fluctuates and gives an erratic pressureapplication which in turn causes a poor weld.

At the end of the completed weld cycle, the speed sensing unit willsignal the electrical controls that the spindle has stopped and theelectrical controls 56 will in turn signal control valves 50, 52 and 54to shift to their original positions. This will close off communicationbetween pump 48 and cylinder 12, and reopen the high pressure signalcommunication between pump 36 and servo valve 26.

At the same time, the flow path between chambers 40 and 44 is closed offby valve 52.

The conversion assembly 10 therefore becomes inactive and the pumpcontrols for the variable displacement pump 36 become active. Theconversion assembly 10 and related controls remain inactive until onceagain it is desirable to convert the variable delivery pump 36 to afixed delivery pump. As was described, this is accomplished at the timethe thrust pressure is applied to the weld pieces. However, there areother operations of the welding machine, such as operating special typesof clamping fixtures, where a fixed delivery from pump 36 would be moredesirable than a variable delivery. The conversion assembly 10 cantherefore be used for these purposes as well as for converting at thetime of axial thrust application.

While we have illustrated and described the preferred embodiments of ourinvention, it is to be understood that these are capable of variationand modification, and we therefore do not wish to be limited to theprecise details set forth, but desire to avail ourselves of such changesand alterations as fall within the purview of the following claims.

What is claimed is:

1. A control for a hydraulic pump of the kind in which the displacementof the pump is varied by changing the angular position of a wobble plateand comprising, a hydraulic servomotor including a servo pistonconnected to the wobble plate, said servomotor having a fluid pressurechamber on each side of the servo piston, servomotor control meansresponsive to the output pressure of the pump for controlling theservomotor to cause the pump to operate as a variable displacement pumpin one condition of operation, and locking means for locking theservomotor in a predetermined position to cause the pump to operate as afixed displacement pump in a second condition of operation, said lockingmeans including disabling means for disabling the servomotor controlmeans,

said disabling means including first valve means for shutting off theflow of pressurized fluid from the pump to the servomotor control meansand second valve means for equalizing the fluid pressures in thechambers of the hydraulic servomotor.

2. A control as defined in claim 1 wherein the locking means include ashaft attached to the servo piston to hold the piston in a fixedposition during the second condition of operation.

3. A control as defined in claim 2 wherein the locking means include ahydraulic motor having piston means for positioning the shaft in thesecond condition of operation.

4. A control for a hydraulic pump of the kind in which the displacementof the pump is varied by changing the angular position of a wobble plateand comprising, a hydraulic servomotor including a servo pistonconnected to the wobble plate, said servomotor having a fluid pressurechamber on each side of the servo piston, servomotor control meansresponsive to the output pressure of the pump for controlling theservomotor to cause the pump to operate as a variable dis placement pumpin one condition of operation, and locking means for locking theservomotor in a predetermined position to cause the pump to operate as afixed displacement pump in a second condition of operation, said lockingmeans including disabling means for disabling the servomotor controlmeans by equalizing the fluid pressures in the chambers of the hydraulicservomotor, a shaft attached to the servo piston to hold the piston in afixed position during the second condition of operation, a hydraulicmotor having piston means for positioning the shaft in the secondcondition of operation and wherein the locking means include a fixedstop, the piston means include a first piston member connected to theshaft and a second floating piston member which engages the stop andstops movement of the first piston and shaft in the second condition ofoperation.

5. A control as defined in claim 4 wherein the connection between theshaft and the first piston member is a threaded connection which isadjustable to vary the position of the servo piston and thus the amountof the fixed output of the pump in the second condition of operation.

* i i i I

1. A control for a hydraulic pump of the kind in which the displacementof the pump is varied by changing the angular position of a wobble plateand comprising, a hydraulic servomotor including a servo pistonconnected to the wobble plate, said servomotor having a fluid pressurechamber on each side of the servo piston, servomotor control meansresponsive to the output pressure of the pump for controlling theservomotor to cause the pump to operate as a variable displacement pumpin one condition of operation, and locking means for locking theservomotor in a predetermined position to cause the pump to operate as afixed displacement pump in a second condition of operation, said lockingmeans including disabling means for disabling the servomotor controlmeans, said disabling means including first valve means for shutting offthe flow of pressurized fluid from the pump to the servomotor controlmeans and second valve means for equalizing the fluid pressures in thechambers of the hydraulic servomotor.
 2. A control as defined in claim 1wherein the locking means include a shaft attached to the servo pistonto hold the piston in a fixed position during the second condition ofoperation.
 3. A control as defined in claim 2 wherein the locking meansinclude a hydraulic motor having piston means for positioning the shaftin the second condition of operation.
 4. A control for a hydraulic pumpof the kind in which the displacement of the pump is varied by changingthe angular position of a wobble plate and comprising, a hydraulicservomotor including a servo piston connected to the wobble plate, saidservomotor having a fluid pressure chamber on each side of the servopiston, servomotor control means responsive to the output pressure ofthe pump for controlling the servomotor to cause the pump to operate asa variable displacement pump in one condition of operation, and lockingmeans for locking the servomotor in a predetermined position to causethe pump to operate as a fixed displacement pump in a second conditionof operation, said locking means including disabling means for disablingthe servomotor control means by equalizing the fluid pressures in thechambers of the hydraulic servomotor, a shaft attached to the servopiston to hold the piston in a fixed position during the secondcondition of operation, a hydraulic motor having piston means forpositioning the shaft in the second condition of operation and whereinthe locking means include a fixed stop, the piston means include a firstpiston member connected to the shaft and a second floating piston memberwhich engages the stop and stops movement of the first piston and shaftin the second condition of operation.
 5. A control as defined in claim 4wherein the connection between the shaft and the first piston member isa threaded connection which is adjustable to vary the position of theservo piston and thus the amount of the fixed output of the pump in thesecond condition of operation.